This invention relates to printing books from scanned pages and particularly concerns aligning the pages in the printed book.
A Portable Document Format (PDF) file is a self-contained cross-platform document. It is a file that will look the same on the screen and in print, regardless of what kind of computer or printer someone is using and regardless of what software package was originally used to create it. A PDF file contains the complete formatting of the original document, including font information and images. A user may compress the PDF file and this allows complex information to be stored, transmitted and downloaded efficiently. The PDF file format was developed by Adobe Systems. PDF captures formatting information from a variety of desktop publishing applications, making it possible to send formatted documents and have them appear on the recipient's monitor or printer as they were intended. The PDF file format captures all the elements of a printed document as an electronic image that can be viewed, navigated, or printed. In the PDF format, all the text information is still available as text, all graphics are still stored as vector graphics, and images are still images. PDF files are more than images of documents. PDF files can have embedded resources, like type fonts so that these resources are available at any viewing location.
PDF files are especially useful for documents such as magazine articles, product brochures, or flyers where a publisher wants to preserve the original graphic appearance online. A PDF file contains one or more page images. A viewer may zoom in on or out from any page and may move forward and backward. Because PDF files are cross platform files, they are widely used in the printing industry. A customer often brings to a printer documents that are in different formats and asks the printer to arrange the documents into a book. Other times a customer has a hard copy of book that he wants to reproduce and the easiest method of reproduction is to copy the pages on a photocopy machine and sort the pages into books.
To scan a book and therefore convert it to an electronic version that can be printed on a production printer, the book is cut at the spine and then scanned page by page. This creates originals that no longer contain perfectly aligned page images. When the raw scan data is printed, the pages appear to “jump” around when one browses through the book. Because of that, there is a need to either automatically or manually align the pages prior to printing. This invention assumes a PDF based workflow. It is also assumed that the application providing these features is implemented as an Acrobat plug-in. All image pre-processing like deskew or despeckle are performed before the pages are aligned in accordance with one of the following procedures. This pre-processing may automatically be initiated by the alignment function before the actual page alignment.